Speaking at an emergency UN Security Council meeting, Nikki Haley said: “We are confident that we have crippled Syria‘s chemical weapons program.
“We are prepared to sustain this pressure, if the Syrian regime is foolish enough to test our will.
“If the Syrian regime uses this poison gas again, the United States is locked and loaded.”
UK ambassador Karen Pierce told the meeting there had been “clear boundaries” in the action that had been taken in an attempt to avoid escalation.
She said repeated attempts to hold the Syrian regime to account had been met with Russian “obstruction and resistance”.
“We have repeatedly in this council attempted to overcome this obstruction, without success,” she said.
“We are faced with a litany of violations, no sense of guilt, no sense of regret, no sense of responsibility, a shameful record wrapped in a mix of denial, deceit and disinformation.”
Ms Pierce added: “I will take no lessons in international law from Russia.”
Ambassador Vassily Nebenzia, Russia’s representative to the UN, accused the US, Britain and France of following a “well tried” pattern of provocation, “mendacious” accusation, verdict and punishment.
He said: “This is hooliganism in international relations, and not minor hooliganism given that we are talking about major nuclear powers.”
Russian foreign minister Sergey Lavrov meanwhile reiterated his claim that the UK was behind the poisoning of Sergei Skripal in Salisbury.
In the first full response from Moscow since last night’s co-ordinated airstrikes by the allied forces, minister Mr Lavrov also hit back at the “incontrovertible facts” the UK, US and France used to justify the strikes in Syria, and said they were not shared with the Russian government.
And he said that the Syrian government is ready to fully co-operate with an investigation into the use of chemical weapons in the city of Douma on April 7.
Following a press conference at Downing Street in which Theresa May linked the Salisbury nerve agent attack on the Skripals and the use of chemical weaponry by Syrian president Bashar Assad, Mr Lavrov again said Russia had evidence the West was responsible.
Highlighting documents presented to Moscow by Swiss researchers, he said: “We have received confidential information and these are questions that have something directly to do with life and death.
Additional reporting by the Press Association